1. Purpose

OREKIT library is a low-level library for space mechanics projects. It is implemented in the JAVA language.

OREKIT project was initiated by CS with the following goals in mind:

provide a common base layer for space projects
support both quick developments with loose requirements and complex projects with rich physical modeling, fine customization, and high accuracy
be user-extensible through clear and as simple as possible architecture
use unified interfaces to allow models and algorithms switching with almost no effort
provide both basic and rich models that can be plugged interchangeably to ease applications validation
separate models configuration from models usage to hide away complexity and keep caller code simple
support both development of standalone and embedded applications (web services, plugins, scripting frameworks...)
use up-to-date techniques for low cost development and maintenance
remove platforms and system dependencies and leverage environment-hell (environment variables, dynamic libraries versions, operating system, filesystem layout...)

2. Features

Orekit can be used for many purposes, from simple geometrical or orbital tools up to complex orbits propagators with several perturbing forces, maneuvers and discrete events. Here is a short list of the features offered by the library:

Time
- high accuracy absolute dates
- time scales (TAI, UTC, UT1, GPS, TT, TCG, TDB, TCB, GMST, GST, GLONASS, QZSS, BDT, IRNSS...)
- transparent handling of leap seconds
- support for CCSDS time code standards
Geometry
- frames hierarchy supporting fixed and time-dependent (or telemetry-dependent) frames
- predefined frames (EME2000/J2000, ICRF, GCRF, all ITRF from 1988 to 2020 and intermediate frames, TOD, MOD, GTOD and TEME frames, Veis, topocentric, tnw and qsw local orbital frames, relative encounter frames, Moon, Sun, planets, solar system barycenter, Earth-Moon barycenter, ecliptic)
- user extensible (used operationally in real time with a set of about 60 frames on several spacecraft)
- transparent handling of IERS Earth Orientation Parameters (for both new CIO-based frames following IERS 2010 conventions and old equinox-based frames)
- transparent handling of JPL DE 4xx (405, 406 and more recent) and INPOP ephemerides
- transforms including kinematic combination effects
- composite transforms reduction and caching for efficiency
- extensible central body shapes models (with predefined spherical and ellipsoidic shapes)
- cartesian and geodesic coordinates, kinematics
- computation of Dilution Of Precision (DOP) with respect to GNSS constellations
- projection of sensor Field Of View footprint on ground for any FoV shape
Spacecraft state
- cartesian, elliptical Keplerian, circular and equinoctial parameters, with non-Keplerian derivatives if available
- Walker constellations (including in-orbit spares with shifted position)
- Two-Line Elements (TLE)
- Two-Line Elements generation using Fixed-Point algorithm or Least Squares Fitting
- transparent conversion between all parameters
- automatic binding with frames
- attitude state and derivative
- jacobians
- mass management
- user-defined associated state (for example battery status, or higher order derivatives, or anything else)
Covariance
- covariance propagation
- covariance extrapolation using a Keplerian model
- covariance frame transformation (inertial, Earth fixed, and local orbital frames)
- covariance type transformation (cartesian, keplerian, circular, and equinoctial)
- covariance interpolation based on the blending model
Maneuvers
- analytical models for small maneuvers without propagation
- impulse maneuvers for any propagator type
- continuous maneuvers for numerical propagator type
- configurable low thrust maneuver model based on event detectors
- used-defined propulsion models intended to be used with maneuver class (constant and piecewise polynomials already provided by the library)
- user-friendly interface for maneuver triggers
Propagation
- analytical propagation models
  - Kepler
  - Eckstein-Heschler
  - Brouwer-Lyddane with Warren Phipps' correction for the critical inclination of 63.4° and the perturbative acceleration due to atmospheric drag
  - SDP4/SGP4 with 2006 corrections
  - GNSS: GPS, QZSS, Galileo, GLONASS, Beidou, IRNSS and SBAS
  - Intelsat's 11 elements
- numerical propagators
  - central attraction
  - gravity models including time-dependent like trends and pulsations (automatic reading of ICGEM (new Eigen models), SHM (old Eigen models), EGM, SHA (GRGM1200B and GRGM1200L) and GRGS gravity field files formats, even compressed)
  - atmospheric drag
  - third body attraction (with data for Sun, Moon and all solar systems planets)
  - radiation pressure with eclipses (multiple oblate spheroids occulting bodies, multiple coefficients for bow and wing models)
  - solid tides, with or without solid pole tide
  - ocean tides, with or without ocean pole tide
  - general relativity (including Lense-Thirring and De Sitter corrections)
  - Earth's albedo and infrared
  - multiple maneuvers
  - empirical accelerations to account for the unmodeled forces
  - state of the art ODE integrators (adaptive stepsize with error control, continuous output, switching functions, G-stop, step normalization...)
  - serialization mechanism to store complete results on persistent storage for later use
  - propagation in non-inertial frames (e.g. for Lagrange point halo orbits)
- semi-analytical propagation model (DSST) with customizable force models
  - central attraction
  - gravity models
  - J2-squared effect (Zeis model)
  - atmospheric drag
  - third body attraction
  - radiation pressure with eclipse
- computation of Jacobians with respect to orbital parameters and selected force models parameters
- trajectories around Lagragian points using CR3BP model
- tabulated ephemerides
  - file based
  - memory based
  - integration based
- Taylor-algebra (or any other real field) version of most of the above propagators, with all force models, events detection, orbits types, coordinates types and frames allowing high order uncertainties and derivatives computation or very fast Monte-Carlo analyzes
- unified interface above analytical/numerical/tabulated propagators for easy switch from coarse analysis to fine simulation with one line change
- all propagators can manage the time loop by themselves and handle callback functions (called step handlers) from the calling application at each time step
  - step handlers can be called at discrete time at regular time steps, which are independent of propagator time steps
  - step handlers can be called with interpolators valid throughout one propagator time step, which can have varying sizes
  - step handlers can be switched off completely, when only final state is desired
  - special step handlers are provided for a posteriori ephemeris generation: all intermediate results are stored during propagation and provided back to the application which can navigate at will through them, effectively using the propagated orbit as if it was analytical model, even if it really is a numerically propagated one, which is ideal for search and iterative algorithms
  - several step handlers can be used simultaneously, so it is possible to have a fine grained fixed time step to log state in a huge file, and have at the same time a coarse grained time step to display progress for user at a more human-friendly rate, this feature can also be used for debugging purpose, by setting up a temporary step handler alongside the operational ones
- handling of discrete events during integration (models changes, G-stop, simple notifications...)
- adaptable max checking interval for discrete events detection
- predefined discrete events
  - eclipse (both umbra and penumbra)
  - ascending and descending node crossing
  - anomaly, latitude argument or longitude argument crossings, with either true, eccentric or mean angles
  - apogee and perigee crossing
  - alignment with some body in the orbital plane (with customizable threshold angle)
  - angular separation thresholds crossing between spacecraft and a beacon (typically the Sun) as seen from an observer (typically a ground station)
  - raising/setting with respect to a ground location (with customizable triggering elevation and ground mask, optionally considering refraction)
  - date and on-the-fly resetting countdown
  - date interval with parameter-driven boundaries
  - latitude, longitude, altitude crossing
  - latitude, longitude extremum
  - elevation extremum
  - moving target detection (with optional radius) in spacecraft sensor Field Of View (any shape, with special case for circular)
  - spacecraft detection in ground based Field Of View (any shape)
  - sensor Field Of View (any shape) overlapping complex geographic zone
  - complex geographic zones traversal
  - inter-satellites direct view (with customizable skimming altitude)
  - ground at night
  - impulse maneuvers occurrence
  - geomagnetic intensity
  - extremum approach for TCA (Time of Closest Approach) computing
  - beta angle
  - relative distance with another object
- possibility of slightly shifting events in time (for example to switch from solar pointing mode to something else a few minutes before eclipse entry and reverting to solar pointing mode a few minutes after eclipse exit)
- events filtering based on their direction (for example to detect only eclipse entries and not eclipse exits)
- events filtering based on an external enabling function (for example to detect events only during selected orbits and not others)
- events combination with boolean operators
- ability to run several propagators in parallel and manage their states simultaneously throughout propagation
Attitude
- extensible attitude evolution models
- predefined laws
  - central body related attitude (nadir pointing, center pointing, target pointing, yaw compensation, yaw-steering)
  - orbit referenced attitudes (LOF aligned, offset on all axes)
  - space referenced attitudes (inertial, celestial body-pointed, spin-stabilized)
  - attitude aligned with one target and constrained by another target
  - tabulated attitudes, either respective to inertial frame or respective to Local Orbital Frames
  - specific law for GNSS satellites: GPS (block IIA, block IIF, block IIF), GLONASS, GALILEO, BEIDOU (GEO, IGSO, MEO)
  - torque-free for general (non-symmetrical) body
- loading and writing of CCSDS Attitude Data Messages (both AEM, APM and ACM types are supported, in both KVN and XML formats, standalone or in combined NDM)
- exporting of attitude ephemeris in CCSDS AEM and ACM file format
Orbit determination
- batch least squares fitting
  - optimizers choice (Levenberg-Marquardt or Gauss-Newton)
  - decomposition algorithms choice (QR, LU, SVD, Cholesky)
  - choice between forming normal equations or not
- sequential batch least squares
  - sequential Gauss-Newton optimizer
  - decomposition algorithms choice (QR, LU, SVD, Cholesky)
  - possibility to use an initial covariance matrix
- Kalman filtering
  - customizable process noise matrices providers
  - time dependent process noise provider
  - implementation of the Extended Kalman Filter
  - implementation of the Extended Semi-analytical Kalman Filter (ESKF)
  - implementation of the Unscented Kalman Filter
  - implementation of the Unscented Semi-analytical Kalman Filter
- parameters estimation
  - orbital parameters estimation (or only a subset if desired)
  - force model parameters estimation (drag coefficients, radiation pressure coefficients, central attraction, maneuver thrust, flow rate or start/stop epoch)
  - measurements parameters estimation (biases, satellite clock offset, station clock offset, station position, pole motion and rate, prime meridian correction and rate, total zenith delay in tropospheric correction)
- orbit determination can be performed with numerical, DSST, SDP4/SGP4, Eckstein-Hechler, Brouwer-Lyddane, or Keplerian propagators
- ephemeris-based orbit determination to estimate measurement parameters like station biases or clock offsets
- multi-satellites orbit determination
- initial orbit determination methods (Gibbs, Gooding, Lambert, Gauss, and Laplace)
- ground stations displacements due to solid tides
- ground stations displacements due to ocean loading (based on Onsala Space Observatory files in BLQ format)
- ground stations displacements due to plate tectonics
- several predefined measurements
  - range
  - range rate (one way and two way)
  - turn-around range
  - azimuth/elevation
  - right ascension/declination
  - position-velocity
  - position
  - inter-satellites range (one way and two way)
  - inter-satellites GNSS one way range rate
  - inter-satellites GNSS phase
  - GNSS code
  - GNSS phase with integer ambiguity resolution and wind-up effect
  - Time Difference of Arrival (TDOA)
  - Frequency Difference of Arrival (FDOA)
  - Bi-static range and range rate
  - multiplexed
- possibility to add custom measurements
- loading of ILRS CRD laser ranging measurements file
- loading and writing of CCSDS Tracking Data Messages (in both KVN and XML formats, standalone or in combined NDM)
- several predefined modifiers
  - tropospheric effects
  - ionospheric effects
  - clock relativistic effects (including J2 correction)
  - station offsets
  - biases
  - delays
  - Antenna Phase Center
  - Phase ambiguity
  - Shapiro relativistic effect
  - aberration of light in telescope measurements
- possibility to add custom measurement modifiers (even for predefined events)
- combination of GNSS measurements
  - dual frequency combination of measurements (Geometry-free, Ionosphere-free, Narrow-lane, Wide-lane and Melbourne-Wübbena)
  - single frequency combination of measurements (Phase minus code and GRAPHIC)
- measurements generation
  - with measurements feasibility triggered by regular event detectors (ground visibility, ground at night, sunlit satellite, inter satellites direct view, boolean combination...)
  - with measurement scheduling as fixed step streams (optionally aligned with round UTC time)
  - with measurement scheduling as high rate bursts rest periods (optionally aligned with round UTC time)
  - possibility to customize measurement scheduling
GNSS
- computation of Dilution Of Precision
- loading of ANTEX antenna models file
- loading and writing of RINEX observation files (version 2, 3, and 4)
- loading of RINEX navigation files (version 2, 3, and 4)
- support for Hatanaka compact RINEX format
- loading of SINEX file (can load station positions, velocities, eccentricities, Post-Seismic Deformation models, EOPs, and Differential Code Biases)
- loading of RINEX clock files (version 2 and version 3)
- parsing of IGS SSR messages for all constellations (version 1)
- parsing of RTCM messages (both ephemeris and correction messages)
- parsing of GPS RF link binary message
- Hatch filters for GNSS measurements smoothing
- implementation of Ntrip protocol
- decoding of GPS navigation messages
Orbit file handling
- loading and writing of SP3 orbit files (from versions a to d, including extension to a few inertial frames)
- splicing and interpolation of SP3 files
- loading and writing of CCSDS Orbit Data Messages (both OPM, OEM, OMM, OCM types are supported, in both KVN and XML formats, standalone or in combined NDM)
- loading of SEM and YUMA files for GPS constellation
- exporting of ephemeris in CCSDS OEM and OCM file formats
- loading of ILRS CPF orbit files
- exporting of ephemeris in STK format
Earth models
- atmospheric models (DTM2000, Jacchia-Bowman 2008, NRL MSISE 2000, Harris-Priester and simple exponential models), and Marshall solar Activity Future Estimation, optionally with lift component
- support for CSSI space weather data
- support for SOLFSMY and DTC data for JB2008 atmospheric model
- tropospheric delay (modified Saastamoinen, estimated, fixed)
- tropospheric mapping functions (Vienna 1, Vienna 3, Global, Niell)
- tropospheric refraction correction angle (Recommendation ITU-R P.834-7 and Saemundssen's formula quoted by Meeus)
- tropospheric model for laser ranging (Marini-Murray, Mendes-Pavlis)
- Klobuchar ionospheric model (including parsing α and β coefficients from University of Bern Astronomical Institute files)
- Global Ionospheric Map (GIM) model
- NeQuick ionospheric model
- VTEC estimated ionospheric model with Single Layer Model (SLM) ionospheric mapping function
- Global Pressure and Temperature models (GPT, GPT2, GPT2w, GPT3)
- geomagnetic field (WMM, IGRF)
- geoid model from any gravity field
- displacement of ground points due to tides
- tessellation of zones of interest as tiles
- sampling of zones of interest as grids of points
- construction of trajectories using loxodromes (commonly, a rhumb line)
Indirect optimal control
- adjoint equations as defined by Pontryagin's Maximum Principle with Cartesian coordinates for a range of forces: (gravitational, inertial) including J2
- so-called energy cost functions (proportional to the integral of the control vector's squared norm), with Hamitonian evaluation
- single shooting based on Newton algorithm for the case of fixed time, fixed Cartesian bounds
Collisions
- loading and writing of CCSDS Conjunction Data Messages (CDM in both KVN and XML formats)
- 2D probability of collision computing methods assuming short term encounter and spherical bodies:
  - Chan 1997
  - Alfriend 1999
  - Alfriend 1999 (maximum version)
  - Alfano 2005
  - Patera 2005 (custom Orekit implementation) (recommended)
  - Laas 2015 (recommended)
Customizable data loading
- loading by exploring folders hierarchy on local disk
- loading from explicit lists of files on local disk
- loading from classpath
- loading from network (even through internet proxies)
- support for zip archives
- automatic decompression of gzip compressed (.gz) files upon loading
- automatic decompression of Unix compressed (.Z) files upon loading
- automatic decompression of Hatanaka compressed files upon loading
- plugin mechanism to add filtering like custom decompression algorithms, deciphering or monitoring
- plugin mechanism to delegate loading to user defined database or data access library

3. Dependency

OREKIT has only one dependency: the Hipparchus open-source library. This library provides mathematical tools for many purposes: geometry, polynomial equations, differential equations, and more... It is distributed under the business-friendly Apache Software License version 2.0.

OREKIT is based on several Hipparchus packages:

geometry, which provides very useful objects as vectors and rotations (internally represented by quaternions)
ode, which provides numerical solutions to solve Ordinary Differential Equations (ODE)
optim, which provides multi-dimensional optimization
solvers, which provides root-finding algorithms
differentiation, which provides analytical computation of partial derivatives to arbitrary order and arbitrary number of free parameters

The use of Hipparchus is hidden in OREKIT as much as possible so users don't need to fully master this library. If they wish, they can limit themselves to understanding the simple classes Vector3D and Rotation from the geometry package, and the interface FirstOrderIntegrator from the ode package.

Packages
Package	Description
org.orekit.annotation	This package is the top level package for Orekit's specific annotations.
org.orekit.attitudes	This package provides classes to represent simple attitudes.
org.orekit.bodies	This package provides interface to represent the position and geometry of space objects such as stars, planets or asteroids.
org.orekit.compiler.plugin	This package provides elements to handle data context plugin.
org.orekit.control	This package provides routines to perform optimal control within the frame of orbital mechanics.
org.orekit.control.indirect	This package provides routines to perform so-called indirect optimal control within the frame of orbital mechanics.
org.orekit.control.indirect.adjoint	This package provides routines to model the adjoint dynamics as in the Pontryagin Maximum Principle, as used in indirect control.
org.orekit.control.indirect.adjoint.cost	This package provides routines to model the control cost in adjoint equations as in the Pontryagin Maximum Principle.
org.orekit.control.indirect.shooting	This package provides routines to solve indirect optimal control within the frame of orbital mechanics, using shooting methods.
org.orekit.control.indirect.shooting.boundary	This package provides classes relative to the boundary conditions for indirect shooting.
org.orekit.control.indirect.shooting.propagation	This package provides classes relative to the propagation part of indirect shooting.
org.orekit.data	This package provide base classes for exploring the configured data directory tree and read external data that can be used by the library.
org.orekit.errors	This package provides classes to generate and handle exceptions.
org.orekit.estimation	This package is the top level package for orbit determination.
org.orekit.estimation.iod	This package provides initial orbit determination methods.
org.orekit.estimation.leastsquares	The leastsquares package provides an implementation of a batch least squares estimator engine to perform an orbit determination.
org.orekit.estimation.measurements	The measurements package defines everything that is related to orbit determination measurements.
org.orekit.estimation.measurements.filtering	This package provides measurement pre-processing filters.
org.orekit.estimation.measurements.generation	This package provides Orbit Determination measurements generation.
org.orekit.estimation.measurements.gnss	This package provides methods to handle GNSS measurements.
org.orekit.estimation.measurements.modifiers	This package provides measurement modifier.
org.orekit.estimation.sequential	The sequential package provides an implementation of a Kalman Filter engine to perform an orbit determination.
org.orekit.files	Top level package for various parsers.
org.orekit.files.ccsds	This package is gathers sub-packages providing parsers/writers for various CCSDS messages.
org.orekit.files.ccsds.definitions	This package contains definitions for CCSDS objects (frames, time systems...).
org.orekit.files.ccsds.ndm	This package contains the base hierarchy for CCSDS ADM, ODM and TDM.
org.orekit.files.ccsds.ndm.adm	This package contains class managing CCSDS Attitude Data Message.
org.orekit.files.ccsds.ndm.adm.acm	This package contains class managing CCSDS Attitude Comprehensive Message.
org.orekit.files.ccsds.ndm.adm.aem	This package contains class managing CCSDS Attitude Ephemeris Message.
org.orekit.files.ccsds.ndm.adm.apm	This package contains class managing CCSDS Attitude Parameter Message.
org.orekit.files.ccsds.ndm.cdm	This package contains class managing CCSDS Conjunction Data Message.
org.orekit.files.ccsds.ndm.odm	This package contains class managing CCSDS Orbit Data Message.
org.orekit.files.ccsds.ndm.odm.ocm	This package contains class managing CCSDS Orbit Comprehensive Message.
org.orekit.files.ccsds.ndm.odm.oem	This package contains class managing CCSDS Orbit Ephemeris Message.
org.orekit.files.ccsds.ndm.odm.omm	This package contains class managing CCSDS Orbit Mean-Elements Message.
org.orekit.files.ccsds.ndm.odm.opm	This package contains class managing CCSDS Orbit Parameter Message.
org.orekit.files.ccsds.ndm.tdm	This package contains class managing CCSDS Tracking Data Message.
org.orekit.files.ccsds.section	This package contains class managing the sections in CCSDS Messages.
org.orekit.files.ccsds.utils	This package contains utilities shared by many CCSDS messages parsers/writers.
org.orekit.files.ccsds.utils.generation	This package contains utilities for CCSDS messages generation.
org.orekit.files.ccsds.utils.lexical	This package contains utilities for CCSDS messages lexical analysis.
org.orekit.files.ccsds.utils.parsing	This package contains classes related to the processing of parse tokens using the state design pattern.
org.orekit.files.general	This package provides interfaces for orbit file representations and corresponding parsers.
org.orekit.files.ilrs	This package provides parsers for laser ranging data stored in CDR and CPF formats.
org.orekit.files.rinex	This package is gathers sub-packages providing parsers/writers for various RINEX files.
org.orekit.files.rinex.clock	This package provides classes related to navigation clock files.
org.orekit.files.rinex.navigation	This package provides classes related to RINEX navigation files.
org.orekit.files.rinex.observation	This package provides classes related to RINEX observation files.
org.orekit.files.rinex.section	This package contains class managing the sections in RINEX files.
org.orekit.files.rinex.utils	This package contains utilities shared by many RINEX parsers/writers.
org.orekit.files.rinex.utils.parsing	This package contains classes related to the parsing of RINEX files.
org.orekit.files.sinex	This package provides classes related to station data.
org.orekit.files.sp3	This package provides a parser for orbit data stored in SP3 format.
org.orekit.files.stk	This package provides a parser for STK ephemeris files.
org.orekit.forces	This package provides the interface for force models that will be used by the `NumericalPropagator`, as well as some classical spacecraft models for surface forces (spherical, box and solar array ...).
org.orekit.forces.drag	This package provides all drag-related forces.
org.orekit.forces.empirical	This package provides empirical forces.
org.orekit.forces.gravity	This package provides all gravity-related forces.
org.orekit.forces.gravity.potential	This package provides classes to read gravity field files and supports several different formats.
org.orekit.forces.inertia	This package provides inertial force model.
org.orekit.forces.maneuvers	This package provides models of simple maneuvers.
org.orekit.forces.maneuvers.jacobians	Generators for columns of Jacobian matrices related to maneuver parameters.
org.orekit.forces.maneuvers.propulsion	This package provides propulsion models intended to be used with class `Maneuver`.
org.orekit.forces.maneuvers.trigger	This package provides maneuver triggers' models intended to be used with class `Maneuver`.
org.orekit.forces.radiation	This package provides all radiation pressure related forces.
org.orekit.frames	This package provides classes to handle frames and transforms between them.
org.orekit.frames.encounter	Package specific to encounter local orbital frame.
org.orekit.geometry.fov	This package provides classes for representing a spacecraft sensor Field Of View.
org.orekit.gnss	This package provides classes related to GNSS applications.
org.orekit.gnss.antenna	This package provides classes related to receiver and satellites antenna modeling.
org.orekit.gnss.attitude	This package provides classes related to navigation satellites attitude modeling.
org.orekit.gnss.metric	This package provides classes related to IGS binary formats.
org.orekit.gnss.metric.messages	This package provides all supported IGS binary `messages`.
org.orekit.gnss.metric.messages.common	This package contains utility classes relate to RTCM ephemeris messages.
org.orekit.gnss.metric.messages.rtcm	This package provides all supported RTCM `messages`.
org.orekit.gnss.metric.messages.rtcm.correction	This package provides all supported RTCM correction `messages`.
org.orekit.gnss.metric.messages.rtcm.ephemeris	This package provides all supported RTCM ephemeris `messages`.
org.orekit.gnss.metric.messages.ssr	This package provides all supported IGS SSR `messages`.
org.orekit.gnss.metric.messages.ssr.igm	This package provides all supported IGS Generic SSR Message types.
org.orekit.gnss.metric.messages.ssr.subtype	This package provides all supported IGS SSR Sub-Type Message.
org.orekit.gnss.metric.ntrip	This package provides streams reading from ntrip casters.
org.orekit.gnss.metric.parser	This package provides the top level `MessagesParser` class that can extract `messages` from binary containers like `ByteArrayEncodedMessages` or {link org.orekit.metric.gnss.ssr.parser.InputStreamEncodedMessages InputStreamEncodedMessages}.
org.orekit.gnss.rflink	This package provides classes related to RF-links binary formats.
org.orekit.gnss.rflink.gps	This package provides classes related to GPS RF-links binary formats.
org.orekit.models	Top level package for physical models.
org.orekit.models.earth	This package provides models that simulate certain physical phenomena of Earth and the near-Earth environment.
org.orekit.models.earth.atmosphere	This package provides the atmosphere model interface and several implementations.
org.orekit.models.earth.atmosphere.data	This package provides classes to get atmospheric data, including solar flux and planetary geomagnetic indices.
org.orekit.models.earth.displacement	This package provides models computing reference points displacements on Earth surface.
org.orekit.models.earth.ionosphere	This package provides models that simulate the impact of the ionosphere.
org.orekit.models.earth.tessellation	This package provides ways to do tessellation and sampling of zones of interest over an ellipsoid surface.
org.orekit.models.earth.troposphere	This package provides models that simulate the impact of the troposphere.
org.orekit.models.earth.weather	This package provides models that simulate global weather conditions on Earth.
org.orekit.models.earth.weather.water	This package provides models that convert between relative humidity and partial water pressure.
org.orekit.orbits	This package provides classes to represent orbits.
org.orekit.propagation	Propagation
org.orekit.propagation.analytical	Top level package for analytical propagators.
org.orekit.propagation.analytical.gnss	This package provides classes to propagate GNSS orbits.
org.orekit.propagation.analytical.gnss.data	This package provides classes related to navigation data containing in GNSS almanacs and navigation messages.
org.orekit.propagation.analytical.intelsat	This package provides classes to propagate Intelsat's 11 elements.
org.orekit.propagation.analytical.tle	This package provides classes to read and extrapolate tle's.
org.orekit.propagation.analytical.tle.generation	This package provides classes related to TLE generation.
org.orekit.propagation.conversion	This package provides tools to convert a given propagator or a set of `SpacecraftState` into another propagator.
org.orekit.propagation.conversion.averaging	This package wraps methods from various (semi)analytical models in Orekit to convert back and forth between an averaged orbital state and an osculating one.
org.orekit.propagation.conversion.averaging.converters	This package wraps conversions from an osculating orbit to an averaged state according to a given theory (usually via a fixed-point algorithm using the inverse conversion).
org.orekit.propagation.conversion.averaging.elements	This package contains data classes representing averaged orbital elements (not time-stamped and in any theory compatible with this choice of coordinates).
org.orekit.propagation.events	This package provides interfaces and classes dealing with events occurring during propagation.
org.orekit.propagation.events.handlers	This package provides an interface and classes dealing with events occurrence only.
org.orekit.propagation.events.intervals	This package provides built-in implementations of `AdaptableInterval`.
org.orekit.propagation.integration	Utilities for integration-based propagators (both numerical and semi-analytical).
org.orekit.propagation.numerical	Top level package for numerical propagators.
org.orekit.propagation.numerical.cr3bp	Top level package for CR3BP Models used with a numerical propagator.
org.orekit.propagation.sampling	This package provides interfaces and classes dealing with step handling during propagation.
org.orekit.propagation.semianalytical	Top level package for semi-analytical propagators.
org.orekit.propagation.semianalytical.dsst	This package provides an implementation of the Draper Semi-analytical Satellite Theory (DSST).
org.orekit.propagation.semianalytical.dsst.forces	This package provides force models for Draper Semi-analytical Satellite Theory (DSST).
org.orekit.propagation.semianalytical.dsst.utilities	This package provides utilities for Draper Semi-analytical Satellite Theory (DSST).
org.orekit.propagation.semianalytical.dsst.utilities.hansen	This package provides Hansen coefficient related utilities for Draper Semi-analytical Satellite Theory (DSST).
org.orekit.ssa	Top level package for various space situational awareness fields as well as associated evaluation metrics.
org.orekit.ssa.collision.shorttermencounter.probability.twod	Package specific to calculus assuming a 2D short-term encounter model.
org.orekit.ssa.metrics	This package stores space situational awareness evaluation metrics.
org.orekit.time	This independent package provides classes to handle epochs, time scales, and to compare instants together.
org.orekit.utils	This package provides useful objects.
org.orekit.utils.units	This package provides very basic handling of units.

OREKIT 12.2.1 API

1. Purpose

2. Features

3. Dependency